1. Field Of The Invention
The present invention relates to an overhead obstruction sensing device for motor vehicles and the like which provides an audible and/or visual alarm in the case of contact with an overhead obstruction.
2. Description Of The Related Art
Motor vehicles and, in particular, semitrailer trucks are constantly troubled with insufficient overhead clearance when passing under overhead obstructions such as bridges, loading docks, tree branches, and overhead wires In view of the danger and monetary damages associated with motor vehicles coming into contact with overhead obstructions, sensing devices have been developed for warning of potential contact with an overhead obstruction.
For example, U.S. Pat. No. 4,307,375 describes a sensing device which includes a vertically adjustable metal shaft mounted on a motor vehicle forward of the highest point on the motor vehicle. The metal shaft is connected to a microswitch device which is actuated upon deflection of the metal shaft by contact with an overhead obstruction. The height of the metal shaft is adjusted to match the height of the motor vehicle. The micro-switch device, if actuated, allows current to flow to an alarm thereby warning the operator that the overhead clearance is insufficient.
Conventional sensing devices, however, are difficult to adjust vertically, and it has heretofore been difficult to match the height of the motor vehicle to the height of the metal shaft. In addition, because such sensing devices operate by contacting overhead obstructions, there is danger if the overhead obstruction is a high-tension power line or the like.